U.S. patent number 5,659,566 [Application Number 08/321,774] was granted by the patent office on 1997-08-19 for semiconductor laser module and method of assembling semiconductor laser module.
This patent grant is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Akira Takemoto.
United States Patent |
5,659,566 |
Takemoto |
August 19, 1997 |
**Please see images for:
( Certificate of Correction ) ** |
Semiconductor laser module and method of assembling semiconductor
laser module
Abstract
In a semiconductor laser module, a semiconductor laser element
is disposed on a side surface of a submount perpendicular to a
front surface of a pedestal. The semiconductor laser element, the
submount, a lens, and an optical fiber are positioned on the front
surface of the pedestal so that laser light emitted from the
semiconductor laser element is applied through the lens to a
prescribed portion of the optical fiber with high reliability.
Positioning of the laser element in the direction perpendicular to
the front surface of the pedestal is facilitated, and positioning
accuracy is improved, resulting in a low-cost and high-performance
semiconductor laser module.
Inventors: |
Takemoto; Akira (Itami,
JP) |
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
17278562 |
Appl.
No.: |
08/321,774 |
Filed: |
October 12, 1994 |
Foreign Application Priority Data
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|
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Oct 13, 1993 [JP] |
|
|
5-255423 |
|
Current U.S.
Class: |
372/50.23;
385/14; 385/92; 385/93; 385/49 |
Current CPC
Class: |
H01S
5/02326 (20210101); G02B 6/4224 (20130101); G02B
6/4204 (20130101); H01L 2224/48463 (20130101); H01L
2224/49107 (20130101); G02B 6/4227 (20130101); H01S
5/02251 (20210101) |
Current International
Class: |
G02B
6/42 (20060101); H01S 5/00 (20060101); H01S
5/022 (20060101); H01S 5/02 (20060101); G02B
006/26 () |
Field of
Search: |
;385/14,49,92,93
;372/43 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0541386 |
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May 1983 |
|
EP |
|
171615 |
|
Jul 1985 |
|
EP |
|
0280305 |
|
Aug 1988 |
|
EP |
|
2547661 |
|
Dec 1984 |
|
FR |
|
3433717 |
|
Sep 1984 |
|
DE |
|
61-87113 |
|
May 1986 |
|
JP |
|
61-264778 |
|
Nov 1986 |
|
JP |
|
3166786 |
|
Jul 1991 |
|
JP |
|
Primary Examiner: Bovernick; Rodney B.
Assistant Examiner: Song; Yisun
Attorney, Agent or Firm: Leydig, Voit & Mayer
Claims
What is claimed is:
1. A semiconductor laser module comprising:
a pedestal having opposite first and second surfaces;
a submount disposed on a part of the first surface of the pedestal
and having a side surface perpendicular to the first surface of the
pedestal;
a semiconductor laser element disposed on the side surface of the
submount and spaced from the first surface of the pedestal whereby
spacing between the first surface of the pedestal and the
semiconductor laser element may be selectively determined and
wherein the semiconductor laser element has a first step on a
surface in contact with the side surface of the submount, the
submount has a second step on the side surface in contact with the
semiconductor laser element, and the semiconductor laser element is
positioned on the side surface of the submount at a fixed height
from the first surface of the pedestal with the first step of the
semiconductor laser element engaging the second step of the
submount;
a lens disposed on the first surface of the pedestal; and
an optical fiber having an optical axis, disposed on the first
surface of the pedestal, and having a light incident facet
transverse to the optical axis wherein the side surface of the
submount is parallel to the optical axis, the semiconductor laser
element is positioned on the submount, and the submount, the lens,
and the optical fiber are positioned relative to the optical axis
so that light emitted from the semiconductor laser element is
applied through the lens to a central region of the light incident
facet of the optical fiber.
2. The semiconductor laser module of claim 1 wherein the
semiconductor laser element includes a marker for positioning on a
side surface that can be observed from above the first surface of
the pedestal.
3. A semiconductor laser module comprising:
a pedestal having opposite first and second surfaces;
a submount disposed on a part of the first surface of the pedestal
and having a side surface perpendicular to the first surface of the
pedestal;
a semiconductor laser element disposed on the the surface of the
submount and spaced from the first surface of the pedestal whereby
spacing between the first surface of the pedestal and the
semiconductor laser element may be selectively determined and
wherein the pedestal includes a projection on a part of the first
surface, the projection having a height and reaching the
semiconductor laser element disposed on the submount, and the
semiconductor laser element is positioned in a direction parallel
to the first surface of the pedestal with the semiconductor laser
element abutting the projection;
a lens disposed on the first surface of the pedestal; and
an optical fiber having an optical axis, disposed on the first
surface of the pedestal, and having a light incident facet
transverse to the optical axis wherein the side surface of the
submount is parallel to the optical axis, the semiconductor laser
element is positioned on the submount, and the submount, the lens,
and the optical fiber are positioned relative to the optical axis
so that light emitted from the semiconductor laser element is
applied through the lens to a central region of the light incident
facet of the optical fiber.
4. The semiconductor laser module of claim 3 wherein the
semiconductor laser element is positioned with a resonator length
direction of the semiconductor laser element perpendicular to the
projection by abutting the semiconductor laser element with the
projection.
5. A method of fabricating a semiconductor laser module
comprising:
preparing a pedestal having opposite first and second surfaces;
fixing a lens on a part of the first surface of the pedestal;
fixing an optical fiber having an optical axis and a light incident
facet transverse to the optical axis on a part of the first surface
of the pedestal so that the light incident facet is opposed to the
lens;
preparing a submount having a side surface and including a second
step, and a semiconductor laser element having opposite front and
rear surfaces a first step on the rear surface, and a light
emitting point;
fixing the semiconductor laser element on the side surface of the
submount with the rear surface of the semiconductor laser element
in contact with the side surface of the submount by engaging the
first step of the laser element with the second step of the
submount; and
putting the submount on the first surface of the pedestal so that
the side surface having the semiconductor laser element is
perpendicular to the first surface of the pedestal and parallel to
the optical axis, and fixing the submount on a part of the first
surface of the pedestal so that the semiconductor laser element is
spaced from the first surface of the pedestal and the light emitted
from the semiconductor laser element is applied through the lens to
a central region of the light incident facet of the optical
fiber.
6. The method of claim 5 including:
forming a first marker indicating the position of the light
emitting point of the semiconductor laser element on a portion of
the front surface of the semiconductor laser element, and forming a
second marker on a portion of an edge of the side surface of the
submount where the semiconductor laser element is to be disposed,
the second marker contacting the first surface of the pedestal when
the submount is mounted on the pedestal; and
mounting the semiconductor laser element on the submount so that
the distance between the first marker of the semiconductor laser
element and the second marker of the submount in a direction
perpendicular to a resonator length direction of the laser element
is equal to a distance from the center of the lens to the first
surface of the pedestal.
7. The method of claim 6 including:
using an optical positioning apparatus, detecting the first marker
of the semiconductor laser element and the second marker of the
submount and thereby determining the position of the semiconductor
laser element on the submount.
8. The method of claim 5 including:
forming a marker for position detection on a side surface of the
semiconductor laser element that can be observed from above the
first surface of the pedestal; and
mounting the submount with the semiconductor laser element on the
first surface of the pedestal so that the marker of the
semiconductor laser element is located at a desired position.
9. A method of fabricating a semiconductor laser module
comprising:
preparing a pedestal having opposite first and second surfaces;
fixing a lens on a part of the first surface of the pedestal;
fixing an optical fiber having an optical axis and a light incident
facet transverse to the optical axis on a part of the first surface
of the pedestal so that the light incident facet is opposed to the
lens;
preparing a submount having a side surface, and a semiconductor
laser element having opposite front and rear surfaces and a light
emitting point;
fixing the semiconductor laser element on the side surface of the
submount with the rear surface of the semiconductor laser element
in contact with the side surface of the submount;
forming a projection on part of the first surface of the
pedestal;
positioning the submount with the semiconductor laser element on
the first surface of the pedestal so that the side surface having
the semiconductor laser element is perpendicular to the first
surface of the pedestal and parallel to the optical axis, by
abutting a part of the semiconductor laser element and the
projection, the projection having a height reaching the
semiconductor laser element; and
fixing the submount on a part of the first surface of the pedestal
so that the semiconductor laser element is spaced from the first
surface of the pedestal and the light emitted from the
semiconductor laser element is applied through the lens to a
central region of the light incident facet of the optical fiber.
Description
FIELD OF THE INVENTION
The present invention relates to a semiconductor laser module that
facilitates positioning of a semiconductor laser element and
improves positioning accuracy. The invention also relates to a
method of assembling the semiconductor laser module.
BACKGROUND OF THE INVENTION
FIG. 7 is a sectional view illustrating a prior art semiconductor
laser module. In FIG. 7, reference numeral 101 designates a
pedestal for supporting a semiconductor laser element and optical
parts. The pedestal 101 comprises Si or the like and has a hole 107
about 100 .mu.m deep. A submount 102 comprising SiC or the like and
having a thickness of 300.about.500 .mu.m is fixed on the pedestal
101. A semiconductor laser element 103 about 100 .mu.m thick is
disposed on the submount 102. Wires 104 and 105 are connected to
the semiconductor laser element 103 and the submount 102,
respectively, and current is supplied to the laser element through
these wires. A spherical lens 106 having a radius of about 300
.mu.m is set in the hole 107 of the pedestal 101. The spherical
lens 106 is positioned by the hole 107. An optical fiber 109 is
fixed on the pedestal 101 via a supporter 108 comprising SiC. The
diameter of the optical fiber 109 is about 100 .mu.m. The optical
fiber includes a core through which light is transmitted. The
diameter of the core is about 10 .mu.m. The core is formed by
doping a center portion of the optical fiber.
A description is given of the assembling process.
Initially, the hole 107 is formed in a prescribed position of the
pedestal 101 by a conventional photolithographic technique, and the
supporter 108 is formed on a prescribed part of the pedestal 101.
The spherical lens 106 is set in the hole 107 and fixed using an
adhesive or solder. The optical fiber 109 is fixed on the supporter
108 using an adhesive or solder. Thereafter, the submount 102 is
fixed on a prescribed part of the pedestal 101 using a solder, such
as Au-Sn, and a semiconductor laser element 103 is fixed on the
submount 102 using a solder, such as Au-Sn. The positioning of the
semiconductor laser element 103 is carried out using a marker
disposed on a prescribed portion of the upper surface of the
semiconductor laser element 103 opposite the laser light emitting
point. Preferably, the marker is a metal film. Thereafter, the
wires 104 and 105 are connected to the semiconductor laser element
103 and the submount 102, respectively, preferably by ultrasonic
heating. The other ends of the wires 104 and 105 are connected to
an external terminal of a voltage supply (not shown).
A description is given of the operation. When a voltage is applied
across the wire 104 connected to an external terminal of the
semiconductor laser element 103 and the wire 105 connected to the
submount 105, current flows through the semiconductor laser element
103, and laser light is emitted from a light emitting point of the
semiconductor laser element 103. The emitted laser light is
collected by the lens 106 and applied to the center of the facet of
the optical fiber 109, i.e., the core of the optical fiber 109.
In the present optical fiber communication, it is possible to
transmit optical signals at a rate exceeding 2.5 G bit/sec by
high-speed on-off switching of the voltage applied across the wires
104 and 105 to change the light intensity, i.e., by direct
modulation.
In the prior art semiconductor laser module, in order to utilize
the emitted laser light from the laser element 103 with high
efficiency, the positions of the semiconductor laser element 103,
the spherical lens 106, and the optical fiber 109 must be precisely
determined so that the laser light emitted from the laser element
103 and collected by the spherical lens 109 is applied to the core
of the optical fiber 109 with high reliability. Therefore, in the
prior art laser module, the semiconductor laser element 103, the
lens 106, and the optical fiber 109 are positioned on the pedestal
101 so that the light emitting point of the semiconductor laser
element 103, the center of the lens 106, and the core of the
optical fiber 109 are arranged in a straight line at prescribed
intervals.
However, since the diameter of the core of the optical fiber 109,
i.e., the effective diameter for transmitting laser light, is only
10 .mu.m, if the precision of the assembly of the laser module is
poor, it is difficult to apply the laser light emitted from the
laser element 103 to the optical fiber 109. In the prior art
semiconductor laser module, when the semiconductor laser element
103 is mounted on the submount 102, the position of the laser
element 103 is observed from above so that the light emitting point
of the semiconductor laser element 103 is disposed on a prescribed
position of the pedestal 101, whereby the positioning accuracy of
the semiconductor laser element 103 in the prescribed direction on
the surface of the pedestal 101 is improved. However, the position
of the light emitting point of the semiconductor laser element 103
in the direction perpendicular to the surface of the pedestal 101
depends on the thickness of the submount 102, the thickness of the
solder connecting the submount 102 and the pedestal 101, the
thickness of the semiconductor laser element 103, and the thickness
of the solder connecting the submount 102 and the semiconductor
laser element 103. Usually, in order to apply the emitted laser
light to the core of the optical fiber 109 with high reliability,
the positioning error of the light emitting point of the
semiconductor laser element 103 in the direction perpendicular to
the surface of the pedestal 101 must be lower than about 10 .mu.m.
However, since the total of the errors in the thickness of the
submount 102, the thickness of the solder connecting the submount
102 and the pedestal 101, the thickness of the semiconductor laser
element 103, and the thickness of the solder connecting the
submount 102 and the semiconductor laser element 103 exceeds 10
.mu.m, the positioning error of the light emitting point exceeds 10
.mu.m. Because of the insufficient positioning precision, the laser
light is not reliably applied to the core of the optical fiber 109,
resulting in poor performance of the semiconductor laser and
variations in the performances of each of a plurality of
semiconductor laser modules.
Further, in this prior art laser module, since solder providing
poor thickness controllability is present at two boundaries between
the submount 102 and the pedestal 101 and between the submount 102
and the semiconductor laser element 103 in the direction
perpendicular to the surface of the pedestal 101, the positioning
precision of the light emitting point of the laser element cannot
be improved.
Although it is possible to improve the processing precision of the
thicknesses of the submount 102 and the semiconductor laser element
103 in order to solve the above-described problems, the improved
processing precision is adverse to mass production, resulting in an
increase in the production cost.
Meanwhile, there is another assembling method of the semiconductor
laser module shown in FIG. 7. In this method, initially, the
submount 102 with the semiconductor laser chip 103 is fixed on the
pedestal 101 having the positioning hole 107 and the supporter 108,
and the wires 104 and 105 are connected to the semiconductor laser
element 103 and the submount 102, respectively, preferably by
ultrasonic heating. Thereafter, the lens 106 is set in the hole 107
of the pedestal 101 and the optical fiber 109 is fixed on the
supporter 108. In this assembling method, the intensity of light
incident on the optical fiber 109 is measured while current flows
through the wires 104 and 105, and the optical fiber 109 is fixed
to the pedestal 101 when the intensity attains a maximum, whereby
the laser light is sufficiently applied to the core of the optical
fiber 109 without improving the processing precision of the
submount 102 and the semiconductor laser element 103. As the
result, a semiconductor laser module with sufficient performance is
obtained. In this prior art method, however, the positioning of the
optical fiber 109 takes about 10 minutes, so that the productivity
is reduced and the cost of the assembly is increased, resulting in
an expensive semiconductor laser module. In addition, since the
laser light incident on the optical fiber 109 has a plurality of
peaks because of scattering of the incident light, it is difficult
to find a true peak of the emitted laser light.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a
high-performance and low-cost semiconductor laser module that
improves the positioning precision of the semiconductor laser
element applying laser light to an optical fiber with high
reliability.
It is another object of the present invention to provide a method
of assembling the semiconductor laser module.
Other objects and advantages of the invention will become apparent
from the detailed description that follows. The detailed
description and specific embodiments described are provided only
for illustration since various additions and modifications within
the scope of the invention will be apparent to those of skill in
the art from the detailed description.
According to a first aspect of the present invention, in a
semiconductor laser module, a semiconductor laser element is
disposed on a side surface of a submount perpendicular to a front
surface of a pedestal, and the submount with the semiconductor
laser element, a lens, and an optical fiber are positioned on the
front surface of the pedestal so that laser light emitted from the
semiconductor laser element is applied through the lens to a
prescribed portion of the optical fiber with high reliability.
Therefore, the positioning of the laser element in the direction
perpendicular to the front surface of the pedestal is facilitated,
and the positioning accuracy is improved, resulting in a low-cost
and high-performance semiconductor laser module.
According to a second aspect of the present invention, the
semiconductor laser element has a step on the surface in contact
with the side surface of the submount, and the submount has a step
on the side surface in contact with the laser element. The step of
the laser element is engaged with the step of the submount, whereby
the laser element is positioned on the side surface of the
submount. Therefore, the positioning of the laser element in the
direction perpendicular to the front surface of the pedestal is
facilitated.
According to a third aspect of the present invention, the pedestal
has a projection in a prescribed position of the front surface. The
semiconductor laser element is disposed on the pedestal so that a
portion of the laser element is in contact with the projection.
Therefore, the positioning of the semiconductor laser element in a
prescribed direction on a plane parallel to the front surface of
the pedestal is facilitated.
According to a fourth aspect of the present invention, a portion of
the front surface and a portion of the resonator facet of the
semiconductor laser element are in contact during production.
Therefore, the semiconductor laser element is easily positioned on
the front surface of the pedestal in the resonator length direction
and in the direction perpendicular to the resonator length
direction.
According to a fifth aspect of the present invention, the
semiconductor laser element has a marker for positioning at the
side surface that can be observed from the front surface of the
pedestal. Therefore, the positioning of the semiconductor laser
element in the direction parallel to the front surface of the
pedestal is facilitated.
According to a sixth aspect of the present invention, a method of
assembling a semiconductor laser module comprises fixing a lens and
an optical fiber on a front surface of a pedestal, fixing a
semiconductor laser element on a side surface of a submount,
disposing the submount with the semiconductor element on the
pedestal so that the side surface of the submount is perpendicular
to the front surface of the pedestal, and positioning the submount
on the front surface of the pedestal so that light emitted from the
semiconductor laser element is applied through the lens to a
prescribed portion of the optical fiber. Therefore, the positioning
of the laser element in the direction perpendicular to the front
surface of the pedestal is facilitated, and the positioning
accuracy is improved, resulting in a low-cost and high-performance
semiconductor laser module.
According to a seventh aspect of the present invention, the
above-described assembling process further includes forming markers
for position detection on a prescribed portion of the upper surface
of the semiconductor laser element and on a prescribed portion on
an edge of the side surface of the submount where the laser element
is to be mounted, and fixing the semiconductor laser element on the
submount so that the distance between the marker of the submount
and the marker of the laser element on a plane perpendicular to the
resonator length direction of the laser element and in the
direction parallel to the side surface of the submount is equal to
the height of the center of the lens from the front surface of the
pedestal. Therefore, the positioning of the semiconductor laser
element in the direction perpendicular to the front surface of the
pedestal is facilitated.
According to an eighth aspect of the present invention, in the
above-described assembling process, the semiconductor laser element
is mounted on the submount using an optical positioning apparatus
that detects the markers of the laser element and the submount and
positions the laser element on the submount according to the
positions of the markers. Therefore, the positioning of the
semiconductor laser element in the direction perpendicular to the
front surface of the pedestal is facilitated, and the positioning
accuracy is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) and 1(b) are a side view and a plan view illustrating a
semiconductor laser module in accordance with a first embodiment of
the present invention.
FIGS. 2(a)-2(d) are diagrams for explaining an assembling method of
the semiconductor laser module according to the first embodiment of
the present invention.
FIG. 3 is a perspective view for explaining an assembling method of
a semiconductor laser module in accordance with a second embodiment
of the present invention.
FIG. 4 is a perspective view for explaining an assembling method of
a semiconductor laser module in accordance with a third embodiment
of the present invention.
FIG. 5 is a perspective view for explaining an assembling method of
a semiconductor laser module in accordance with a fourth embodiment
of the present invention.
FIG. 6 is a perspective view illustrating a semiconductor laser
element included in a semiconductor laser module in accordance with
a fifth embodiment of the present invention.
FIG. 7 is a side view of a semiconductor laser module according to
the prior art.
FIG. 8 is a perspective view illustrating a semiconductor laser
element according to a variation of the fifth embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1(a) and 1(b) are a side view and a plan view illustrating a
semiconductor laser module in accordance with a first embodiment of
the present invention. In the figures, reference numeral 1
designates a pedestal supporting a semiconductor laser element and
optical parts. The pedestal 1 comprises Si having a hole 7 at the
front surface. An optical fiber 9 having a diameter of about 100
.mu.m is fixed on the pedestal 1 via a supporter 8 comprising SiC.
A lens 6 having a radius of about 300 .mu. is set in the hole 7 of
the pedestal 1. Reference numeral 23 designates the center of the
lens 6. The height of the supporter 8 and the depth of the hole 7
are selected so that the center 23 of the lens 6 is coplanar with
the center of the facet of the optical fiber 9 from the front
surface of the pedestal 1. A submount 2 comprising SiC is fixed on
a prescribed portion of the front surface of the pedestal 1 so that
the side surface of the submount 2 is perpendicular to the front
surface of the pedestal 1 and parallel to the optical axis of the
optical fiber 9. The height of the submount 2 from the front
surface of the pedestal 1 is about 450 .mu.m, and the length of the
submount 2 in the direction perpendicular to the optical axis of
the fiber 9 is 300.about.500 .mu.m. A semiconductor laser element 3
comprising InGaAsP and emitting light having a wavelength of 1.3
.mu.m is disposed on the side surface of the submount 2. The
semiconductor laser element 3 has a length of 300 .mu.m in the
resonator length direction, a width of about 300 .mu.m in the
resonator width direction, and a thickness of about 100 .mu.m. The
laser light emitting facet 3a of the semiconductor laser element 3
is in the same plane with a side surface of the submount 2
perpendicular to the optical axis of the optical fiber 9. The laser
light emitting facet 3a and the facet of the optical fiber 9 are
opposed to each other through the lens 6, with a prescribed
interval between them. Wires 4 and 5 are connected to the upper
surface of the laser element 3 and the side surface of the submount
2 where the laser element 3 is present, respectively, and current
is supplied to the laser element 3 through the wires 4 and 5.
The assembling process of the semiconductor laser module according
to the first embodiment of the invention is illustrated in FIGS.
2(a)-2(d). In the figures, the same reference numerals as in FIGS.
1(a)-1(b) designate the same or corresponding parts. Reference
numeral 30 designates a light emitting point of the semiconductor
laser element 3. Reference numeral 20 designates a first reference
point disposed at an end of a surface of the submount 2 where the
laser element 3 is disposed. When the submount 2 is mounted on the
pedestal 1, the first reference point 20 is opposed to the optical
fiber 9 and in contact with the surface of the pedestal 1.
Reference numeral 21 designates a second reference point disposed
on the upper surface of the semiconductor laser element 3,
indicating a position just above the light emitting point 30.
Markers which can be confirmed visually or with a detector are
disposed on the first and second reference points 20 and 21.
Reference numeral 22 designates a third reference point disposed on
a side surface of the laser element 3 indicating a position just
beside the light emitting point 30 of the laser element 3.
Initially, the hole 7 for determining the position of the lens 6 is
formed on the front surface of the pedestal 1 by conventional
photolithographic techniques. Thereafter, using adhesive or the
like, the supporter 8 is fixed on the front surface of the pedestal
1, the lens 6 is set in the hole 7 of the pedestal 1, and the
optical fiber 9 is fixed on the supporter 8.
As illustrated in FIG. 2(a), the positions of the first reference
point 20 of the submount 2 and the second reference point 21 of the
laser element 3 are detected with a microscope and adjusted so that
the distance between the first and second reference points, i.e.,
the height of the reference point 21 from the bottom of the
submount 2, is equal to the height of the center 23 of the lens 6
and to the height of the center of the facet of the optical fiber
9. After the positioning, the laser element 3 is fixed on the
submount 2 using solder. The laser emitting facet of the
semiconductor laser element 3 should be in the same plane with the
side surface of the submount 2 facing the lens 6. Thereafter, as
illustrated in FIG. 2(d), the position of the submount 2 on the
pedestal 1 is determined so that the upper surface of the
semiconductor laser element 3 is perpendicular to the surface of
the pedestal 1, the laser emitting facet of the laser element 3 is
opposed to the facet of the optical fiber 9 through the lens 6, and
the third reference point 22 indicating the position of the light
emitting point 30 of the laser element 3 is on a straight line with
the center 23 of the lens 6 fixed on the pedestal 1 and the center
of the facet of the optical fiber 9. After the positioning, the
submount 2 is fixed on the pedestal 1 using solder.
Thereafter, the wires 4 and 5 are connected to the semiconductor
laser element 3 and the submount 2, respectively, preferably by
ultrasonic heating, completing the semiconductor laser module shown
in FIGS. 1(a)-1(b). The semiconductor laser module is sealed in a
plastic package or a ceramic package.
In this first embodiment of the present invention, since the
semiconductor laser element 3 is disposed on the side surface of
the submount 2 so that the upper surface of the laser element 3 is
perpendicular to the surface of the pedestal 1, the position of the
laser element 3 on the submount 2 is variable in the direction
perpendicular to the surface of the pedestal 1 to adjust the height
of the light emitting point 30 of the laser element 3. In the prior
art semiconductor laser module, the height of the light emitting
point of the laser element 103 depends on the thicknesses of the
laser element 103, the submount 102, and the solder, and these
thicknesses cannot be easily controlled during or after
fabrication, resulting in difficulty in positioning the light
emitting point of the laser element 103 in the direction
perpendicular to the surface of the pedestal 101. On the other
hand, in this first embodiment of the invention, it is possible to
accurately position the light emitting point 30 of the laser
element 3 in the direction perpendicular to the surface of the
pedestal 1 by adjusting the position of the laser element 3 on the
side surface of the submount 2. Therefore, the laser light emitted
from the light emitting point 30 of the laser element 3 is applied
to the optical fiber 9 through the lens 6 with high reliability,
resulting in a high-performance semiconductor laser module.
Further, in the direction perpendicular to the surface of the
pedestal 1, the solder is present only between the pedestal 1 and
the submount 2. Therefore, the error in the positioning precision
of the laser light emitting point 30 in the direction perpendicular
to the surface of the pedestal 1 caused by the solder having a poor
thickness controllability is reduced.
Furthermore, the positioning of the laser light emitting point 30
in the direction parallel to the surface of the pedestal 1 is
carried out in the same way as in the prior art laser module. That
is, the position of the submount 2 with the laser element 3 on the
surface of the pedestal 1 is adjusted using the third reference
point 22 so that the laser light emitting point 30 has a prescribed
position.
FIG. 3 is a perspective view for explaining a process of
positioning a semiconductor laser element on a submount, according
to a second embodiment of the present invention. In the figure, the
same reference numerals as in FIGS. 2(a)-2(d) designate the same or
corresponding parts. Reference numeral 10 designates a magnifying
lens. Reference numeral 11 designates a television camera connected
through a computer (not shown) to an apparatus for mounting the
semiconductor laser element 3 on the submount 2 (not shown). The
lens 10 and the television camera 11 make an optical positioning
apparatus 14, i.e., a vision system. In the above-described first
embodiment of the invention, when the semiconductor laser element 3
is mounted on the submount 2, the position of the laser element 3
on the submount 2 is adjusted manually or by using a mounting
apparatus while observing the positions of the reference point 21
of the laser element 3 and the reference point 20 of the submount 2
with a microscope or the like. On the other hand, in this second
embodiment of the invention, the positioning of these reference
points 21 and 20 is performed with the optical positioning
apparatus 14 comprising the magnifying lens 10 and the television
camera 11.
A description is given of the positioning process using the optical
positioning apparatus 14.
Initially, markers comprising metal films or the like that are
detectable by the television camera 11 are formed on the first
reference point 20 of the submount 2 and on the second reference
point 21 of the laser element 3. The positions of the reference
points 20 and 21 are detected through the lens 10 by the television
camera 11, and the obtained data is sent to the computer. In the
computer, the data is analyzed a software. According to the result
of the analysis, the laser element mounting apparatus (not shown)
is driven so that the reference point 21 of the laser element 3 is
located in a prescribed position relative to the reference point 20
of the submount 2. More specifically, the detection and the
analysis are repeated until the distance between the first and
second reference points 20 and 21, i.e., the height of the
reference point 21 from the bottom of the submount 2, is equal to
the height of the center 23 of the lens 6 and to the height of the
center of the facet of the optical fiber 9. In this way, the light
emitting point 30 of the laser element 3 is accurately positioned
in the direction perpendicular to the surface of the pedestal
1.
As described above, in this second embodiment of the present
invention, the positioning of the semiconductor laser element 3 on
the submount 2 is automatically controlled with high accuracy by
the optical positioning apparatus 14 comprising the magnifying lens
10 and the television camera 11, whereby a high-performance
semiconductor laser module is easily fabricated.
FIG. 4 is a perspective view of a part of a semiconductor laser
module in accordance with a third embodiment of the present
invention. In the figure, a semiconductor laser element 3 is
mounted on a submount 2. The semiconductor laser element 3 has a
step on the rear surface in contact with the submount 2. The step
extends in the resonator length direction of the laser element 3.
The submount 2 has a step engaging the step of the laser element 3
on the surface in contact with the laser element 3. These steps are
formed by a conventional photolithographic technique so that the
light emitting point 30 of the laser element 3 is disposed in a
prescribed position in the direction perpendicular to the surface
of the pedestal 1 when the laser element 3 is mounted on the
submount 1 with the steps engaged. Therefore, the optical detection
of the reference points 20 and 21 as in the above-described first
and second embodiments is dispensed with.
In this third embodiment of the invention, since the positioning of
the semiconductor laser element 3 in the direction perpendicular to
the surface of the pedestal 1 is performed by engaging the step of
the laser element 3 with the step of the submount 2, the optical
detection of the position of the laser element 3 is dispensed with,
whereby the positioning process is simplified. In addition, the
precision of the height of the laser light emitting point 30 from
the surface of the pedestal 1 depends on the processing precision
of the steps. Since the steps are formed by a photolithographic
technique providing a high processing precision, the positioning of
the laser light emitting point 30 is performed with high accuracy.
As the result, a semiconductor laser module with improved
characteristics is achieved.
FIG. 5 is a perspective view illustrating a semiconductor laser
module in accordance with a fourth embodiment of the present
invention. In FIG. 5, the same reference numerals as in FIGS.
1(a)-1(b) designate the same or corresponding parts. Reference
numeral 12 designates a projection disposed on the front surface of
the pedestal 1 for positioning a semiconductor laser element. This
projection 12 is formed by a conventional photolithographic
technique. The height of the projection 12 reaches the
semiconductor laser element 3 disposed on the side surface of the
submount 2 but does not reach the light emitting point 30. The
projection 12 has a groove engaged with a part of the corner of the
laser element 3 between the upper surface and the light emitting
facet. When the laser element 3 is engaged with the groove of the
projection 12, the laser element 3 is positioned on a prescribed
part of the front surface of the pedestal 1 so that the light
emitting point 30 of the laser element 3 is aligned with the center
23 of the lens 6 and the center of the facet of the optical fiber
9. Also in this fourth embodiment, since the optical means for
detecting the reference points is dispensed with, the positioning
of the submount 2 is facilitated.
Further, since the photolithographic technique provides a high
processing precision, the projection 12 is formed on a prescribed
part of the pedestal with high precision, resulting in a
highly-precise positioning of the light emitting point 30 of the
laser element 3. As the result, a semiconductor laser module with
improved characteristics is achieved.
FIG. 6 is a perspective view illustrating a semiconductor laser
element included in a semiconductor laser module in accordance with
a fifth embodiment of the present invention. In the figure, a
semiconductor laser element 3 has a marker 13 for position
detection. Preferably, the marker 13 comprises a metal film.
The process of forming the marker 13 on the semiconductor laser
element 3a will be described.
Initially, a plurality of semiconductor laser elements are formed
on a semiconductor substrate (not shown). Thereafter, a groove is
formed on a prescribed surface of the substrate, preferably by
etching. The surface of the substrate with the groove will be a
side surface of each semiconductor laser element that is observable
when the laser element is disposed on a pedestal. Thereafter, a
plurality of markers 13 are formed on portions of the groove
opposite the light emitting points of the respective laser
elements, followed by cleaving to produce a semiconductor laser
chip 13a shown in FIG. 6.
In this fifth embodiment of the present invention, the positioning
of the semiconductor laser element 3a in the direction parallel to
the surface of the pedestal 1 is performed using the marker 13
formed on the side surface of the laser element 3a. In the
above-described first embodiment, it is sometimes difficult to
detect the position of the reference point 22 using the optical
means because the reference point 22 is on a semiconductor crystal
plane that is not always flat. On the other hand, in this fifth
embodiment, since the marker 13 is employed in place of the
reference point 22, the detection of the light emitting point is
facilitated. As the result, the positioning of the semiconductor
laser element is performed with high accuracy.
Since the marker 13 is disposed only for indicating the position of
the laser light emitting point on the side surface of the laser
element, it may be a part 13a of a metal electrode formed on the
upper surface of the semiconductor laser element 3b as shown in
FIG. 8.
While in the above-described first to fifth embodiments the
semiconductor laser module comprises the Si pedestal, a SiC
submount, an InGaAsP laser element, and an SiC supporter, other
materials may be used as these constituents of the semiconductor
laser module with the same effects as described above.
* * * * *